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CAN Bus is a serial bus protocol designed to allow a vehicle components to communicate with fewer wires. It allows automotive components to share a single or dual-wire networked data bus.
With conventional wiring, each individual electric and electronic component is connected directly to all the sensors and actuators that are needed to either supply the control module with test values, or which are controlled by the control module.
In many cases, this results in very long or redundant wiring. The data bus system affords the following advantages relative to conventional wiring:
- Lower cost of wiring
Wiring from sensors only needs to extend to the nearest control unit, where the monitored data is processed to generate data telegrams for transmission to the CAN data bus. Actuators can also receive control signals from a different control unit, which receives the data telegram through the CAN bus and then uses this information to calculate a control parameter for the actuator. - Improved electromagnetic compatibility (EMC)
- Fewer plug connections
- Fewer pins at control modules
- Weight reduction
- Fewer sensors
Signals from one sensor (e.g. coolant temperature) can be received by several receivers. - Better diagnosis
Since signals from one sensor can be received by several receivers (e.g. vehicle speed signal), it can be assumed if a fault is displayed by all systems which use a particular signal, that the sensor is defective or that the control module which processes the signal is faulty. If only one system displays a fault, although the signal is received by several receivers, it can be assumed that the control module which prepares the signal is faulty or that the actuator is defective. - Fast transfer rates
Up to 1Mbit/s with line lengths up to a maximum of 40 m (Mercedes Benz ME 2.8 systems use transfer rates of 83 kbit/s to 500 kbit/s.) - Several messages can be transferred in succession on the same line
The downside is, pseudo mechanics who hack up a factory wiring harness can cause bizarre drivability issues.
© Marcus B. Fitzhugh 2010